Many functions of modern devices in automotive, consumer and industrial applications, such as computer technology, mobile communications technology, converting electrical energy and driving an electric motor or an electric machine, rely on field effect semiconductor devices.
The energy efficiency of, for example, power converters and motor drivers depends on the performance, in particular on the on-resistance (Ron), of the typically used power semiconductor devices. Furthermore, normally-off operating semiconductor devices are often desirable for safety reasons. Normally-off operating may also reduce the overall power consumption of the semiconductor devices since no static driving power is required.
For silicon DMOS (double-diffused metal-oxide-semiconductor) transistors with operating voltages above about 200 V, the on-resistance is mainly determined by the resistance of the drift region. The doping concentration of the drift region of these transistors is, however, limited to ensure a high enough blocking capability.
Wide band-gap semiconductor materials such as SiC have a higher break-down field than low band-gap semiconductor materials. Accordingly, the resistance of the drift region of wide band-gap semiconductor devices may be reduced. However, the so far realized SiC (silicon carbide) normally-off operating power MOSFETs (metal oxide semiconductor field-effect transistors) typically have a relatively high on-resistance due to the low charge carrier mobility close to the interface between SiC and the widely used gate oxide SiO2 (silicon dioxide). Furthermore, the long term stability and defect density of SiO2 are often unsatisfactory when used as a gate oxide on SiC.